#include<stdio.h>
#include<math.h>

int main(void)
{
	double x1,x2,y1,y2,ans;
	
	scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
	
	ans=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
	
	printf("%.2f",ans);
	
	return 0;
}
